1. Field of the Invention
The present invention relates to an imaging probe for use in an image tester that measures a surface feature based on image data generated when a work is imaged. More particularly, it relates to an imaging probe employed as a measuring probe of a three-dimensional tester so that the three-dimensional tester can serve as the image tester.
2. Description of the Related Art
An image tester employs a CCD camera to take an image of a work directly or through the use of a microscope that magnifies the image. Then, through an image processing and arithmetic processing performed to the image data obtained, it measures dimensions of parts of the work. Such the image tester has a disadvantage because the quality of a light source for illuminating the work varies qualities of the collected image data, such as clearness, and exerts an influence on measurement precision. Therefore, the light source for illuminating the work is required to emit an illuminating light with such directivity and uniformity that allow characteristics of the work to be taken with fidelity.
Currently known illuminations for use in the image tester include a down-projection illumination, which provides a light on a work via an imaging optical system, and a ring illumination, which provides a light around a work from the surrounding of an imaging optical system. The image tester often employs these illuminations together. In each of these illuminations, a halogen lamp is conventionally used for a light source.
In order to use a three-dimensional tester as the image tester, an imaging probe has been employed as a measuring probe of the three-dimensional tester in the art. Most conventional imaging probes are secured on the Z-axis (vertical axis) and therefore can not be changed easily with other probes such as a touch signal probe. Because the imaging probe that employs a halogen lamp as the light source has a relatively larger size. In addition, an optical fiber may be employed for leading a light to the proximity of the work from a light source in order to avoid thermal influence from the light source. Accordingly, the size of and thermal radiation from the light source, as well as a path for introducing the illuminating light, raises a problem on realizing an imaging probe easily detachable.
A mechanism for swaying the imaging probe is further required to allow a sample to be imaged at any given angle. It is difficult to sway the imaging probe, however, because of a problem on a load-carrying capacity of the swaying mechanism in addition to the above problems on illumination (the light source and the light introducing path). Thus, it is hard to realize an imaging probe that can satisfy conditions including a possibility of changing a probe (easy detachability) and of setting any imaging direction.
The present invention has been made in consideration of the above problems and accordingly has an object to provide an imaging probe with a small size, light weight, easy detachability and desirably adjustable imaging direction.
The present invention is directed to an imaging probe attachable to a three-dimensional tester as a measuring probe thereof. The imaging probe comprises a solid state imaging device for imaging a work to generate image data thereof; an imaging optical system for focusing an image of the work on the solid state imaging device; a down-projection illumination source, including at least one semiconductor light-emitting device, for producing a down-projection illumination light to illuminate the work; an illuminating optical system for joining the illumination light from the down-projection illumination source to the imaging optical system in order to lead the illumination light to the work via the imaging optical system; a chassis for supporting the solid state imaging device, imaging optical system, down-projection illumination source and illuminating optical system while retaining a certain positional relation among them; and a housing for accommodating the solid state imaging device, imaging optical system, down-projection illumination source and illuminating optical system supported on the chassis.
In the imaging probe according to the present invention, the solid state imaging device, imaging optical system, down-projection illumination source and illuminating optical system are supported on a chassis and accommodated in a housing while retaining a certain positional relation among them. In particular, the down-projection illumination source consists of the semiconductor light-emitting device(s). Therefore, the light source can be made to have a lighter weight and extremely less heating value than that of the use of a halogen lamp. Thus, the down-projection illumination source can be located in the proximity of other members without any large problem. This reduction of a space for arranging components leads to realization of a small and light imaging probe.
The imaging optical system may include an object lens opposing to the work and a focusing lens for focusing a light reflected from the work and transmitted through the object lens on the solid state imaging device. A half mirror may be located in oblique to the optical axis of the imaging optical system between the object lens and the focusing lens. The illumination light emitted from the down-projection illumination source is led into and reflected at the half mirror to illuminate the work via the object lens.
The imaging probe according to the present invention can be detachably mounted, for example, on a probe head of the three-dimensional tester via a mounting block or shank block. The mounting block may be provided with a connector function for electrically connecting and disconnecting input/output signals and power supplies to the down-projection illumination source and solid state imaging device through attachment to and detachment from the probe head. If the imaging probe is mounted on the probe head via the shank block, the shank block may include a connector for connecting with input/output signals and power supplies to the down-projection illumination source and solid state imaging device independently of the shank block.
In a preferred embodiment of the present invention, the imaging probe may further comprise a ring illumination source, which includes semiconductor light-emitting devices arranged to surround the imaging optical system, for producing a ringed illumination light to illuminate the work from the surrounding of the imaging optical system. In this case, the down-projection illumination source and ring illumination light source are activated selectively or simultaneously. Preferably, the down and/or ring illumination light source may be turned on only when the solid state imaging device is operative to image. Preferably, the illumination light from the down and/or ring illumination light source may be illuminated on the work via a diffusing plate. The down and/or ring illumination source may comprise a plurality of semiconductor light-emitting devices. In this case, the plurality of semiconductor light-emitting devices may be controlled simultaneously, or on a block-by-block basis, or independently to turn on/off or vary brightness. The down and/or ring illumination source may be packaged in a cartridge.
Desirably, the chassis and/or housing may be composed of a magnesium alloy that is light and has a high thermal radiation effect. Preferably, the imaging probe of the present invention may have a weight of 500 grams or less.
Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof.